The present invention relates to optical materials containing a curable fluorine-containing prepolymer, and particularly relates to compositions useful as an optical material and to materials used suitably in the field of optical communication where optical amplification technology is used and in the field where luminous phenomenon is used.
An optical communication system using an optical fiber network enables high speed transmission of a large amount of data. Generally an quartz optical fiber is used as the optical fiber. However recently in plastic optical fiber (POF), a POF called GI (graded index) type POF which has a wide band (400 Mbps for 100 m transmission) and assures a low transmission loss has been developed, and construction of an optical communication network for domestic use is also considered. In the respective fibers, there is a difference in a band width of light for transmission. In the silica fiber, 1,300 nm band and 1,500 nm band are mainly used, and in the plastic (acryl) fiber, 650 nm band is mainly used.
In either of quartz optical fiber and plastic optical fiber, in an optical communication system, there arises an attenuation of an optical signal due to a loss caused at the time of transmission, branching, connection and switching. An attenuation of an optical signal is a problem particularly in case of a long distance transmission. Therefore an optical amplifier is needed to compensate for attenuation of optical signals.
Example of an optical amplifier for an optical communication system using quartz optical fiber network is, for instance, a so-called fiber type optical amplifier disclosed in the bulletin (“Light amplification with Er-doped optical fiber and application thereof”, by Masataka Nakazawa, Applied Physics Vol. 59, No. 9, pp. 1175–1192 (1990)). On this device are applied pumping of electron in Erbium (Er) cation atom by visible or near infrared light and a phenomenon of generating fluorescence having a wavelength of about 1,500 nm band.
On the other hand, a luminant has been put into practical use for an inorganic glass containing a rare earth metal ion and for an electronic device for laser beam. However a present situation is such that because of difficulty in production and processing, applications thereof are limited. Also though a polymer composition is disclosed in JP64-26583A, intensity of luminescence is low.
However in case of an optical amplifier (EDFA) using Er-doped optical fiber, a 20 to 30 m long optical fiber for amplification is necessary to obtain an amplifying gain of 30 dB (1000 times). The reason for this is that for example, while a fiber type optical amplifier for 1,550 nm band uses an erbium ion (Er3+)-doped quartz fiber, if a doping amount is increased, a cluster is formed due to association of doping ions and the amplifying action is lowered. Therefore the doping amount is decreased to 10 to 1,000 ppm and a fiber length is increased to obtain an amplifying action. As mentioned above, in case of a fiber type optical amplifier (glass), there is a limit in shortening a length of interface of the optical amplifier. Namely, there is a limit in down-sizing and cost reduction of the optical amplifier.
Also since a base material is inorganic glass, elasticity and mold-processability have not always been satisfactory.
Further in case of a fiber type optical amplifier (glass), it is difficult to make a flat optical amplifier. This causes a problem when an optical integrated circuit is made using an optical amplifier and other optical devices.
Also in case of an inorganic device as a ruminant, because of difficulty in production and processing, applications thereof are limited.
On the other hand, addition of cation of rare earth element to an organic high molecular weight material has been studied. For example, JP5-86189A discloses polysiloxane in which a rare earth metal ion obtained by using chlorosilane having an organic group and a chloride of rare earth element as starting materials is introduced to a high molecular chain. Also JP5-88026A discloses materials such as polyacrylate and polysiloxane containing a complex such as acetylacetone complex of rare earth metal ion which is excellent in solubility in an organic solvent and oxidation resistance. Further in the preprint of High Molecule Society, Vol.43(1), 29 (1994), a material obtained by synthesizing a rare earth element cation salt of a polymerizable organic acid such as acrylic acid or methacrylic acid and polymerizing or copolymerizing such a monomer carrying a rare earth element cation is reported, in which a cation concentration can be increased to about 10% by weight. By those methods, a rare earth element cation can be added in a high concentration to an organic high molecular weight material excellent in mold processability. However there are disadvantages that the synthesizing process is complicated and may give rise to an economical restriction in industrial application, and resins to be used are limited to those having relatively low heat resistance.
Also in order to enhance dispersibility of a rare earth metal ion in a resin, it is necessary that carboxylic acid groups are introduced in a high concentration to a structure of a polymer constituting an acrylic resin. However such an acrylic resin has a large water absorption and therefore cannot be practically used as an optical material which hates presence of water.
Further heat resistance is not sufficient and during a step for producing an optical amplifier or during use thereof, lowering of amplifying characteristics arises.
Also when light source having wavelength bands of 1,300 nm and 1,500 nm is used, there is a substantial disadvantage that transmittance of light is lowered since a carbon-hydrogen bond and oxygen-hydrogen bond in the organic material absorb light of such bands. Therefore studies have been made with respect to replacement of hydrogen with heavy hydrogen (D) or fluorine. As a result, transparency can be improved to a certain extent, but in case of the replacement with heavy hydrogen, water absorption of the material does not change, and in case of the replacement with fluorine, when the replacement is made to an extent of having an effect on transparency, there are disadvantages that dispersibility of a rare earth metal ion is significantly lowered and also solubility in a solvent is lowered. Also in case of the replacement with fluorine, a glass transition temperature is not increased and the problem with heat resistance cannot be solved. Further for application on a luminant using a luminous phenomenon, there is a problem with light resistance of a polymer to be used.
As mentioned above, all the problems in the fields of optical amplification material and light emission material have not been solved, and novel optical amplification material and light emission material which can solve those problems are desired.